I've read lot of things on the forum about the causes of oil pressure drop, oil level, windage tray, oil pick up height and its related brazing to the pumo body can afflict pressure.
Mine is very good, about 70 when cold and over 35 at idle at operating temperature, the problem pop out when engine turns close to 5000 rpm, the gauge pointer has a superfast vibration from around 5 to 35 PSI.
Cavitation?
Looking for the cause on the web i've seen that some oil pump has problem over 5000rpm or so, any experience with them?

i'll tear down oil pan to check pick up height first (honestly i want to see bearings too) then braze the pick up or make a bracket for it.

if me i wouldnt get excited until you actually get her on the road and driving, one thing is if your just sitting and revving theres no load and no real world effects on the engine. get it on the road drive it easily for a bit till your comfortable with how it runs and start getting into the throttle little bit at a time and closely monitor your pressure and temperature.. every engine i build gets the pickup tack welded. (be sure to remove the cotter pin and spring from pump the heat from welding has been known to distort the spring).how many rpm is the motor intended to run? and what are your driving habits? for sb's i like to use the m55hv pump with purple spring(70psi),is that what you have?also if the problem persists after you have it on the road,try another(mechanical) gauge.i hope that helps ease your mind, i know how it can be time/money= edgy.. for the most part sb's are very reliable and forgiving if well maintained and not abused...

thank you for the reply, i'm with you about real life so i have to put my junk on the road before, but... what will happen if engine will run approx 5000 for seconds? i'm concern about that, revving it up is relatively safe, i guess it wouldn't the same thing when the load is on it.
Pump M55 is supposed to be the stock replacement for the SB chevy and i would stay far away from any high volume or pressure pump with stock clearance engine like mine, i think it's gonna be just too much load on cam and distributor gears.
My pump works pretty good until 5000 rpm and i can't understand the why, befoe to get crazy with this and that i want to know if anybody has experienced issue like mine, i wan't to make sure if is just a Melling pump problem before.

i understand your concern, so for now go find yourself a mechanical gauge and see what you get. as far as the hv thing goes, you'll always get a mixed bag of people and suggestions when it comes to hv pumps, but as long as clearances are within tolerance then i will always use a hv pump on a street motor.if you did the cam breakin you should change your oil, i would use a straight viscosity unless its real cold where you are, try 30 wt.

i understand your concern, so for now go find yourself a mechanical gauge and see what you get. as far as the hv thing goes, you'll always get a mixed bag of people and suggestions when it comes to hv pumps, but as long as clearances are within tolerance then i will always use a hv pump on a street motor.

definately, i want to try with a mechanical gauge and see for any difference, thank you.

I've read lot of things on the forum about the causes of oil pressure drop, oil level, windage tray, oil pick up height and its related brazing to the pumo body can afflict pressure.
Mine is very good, about 70 when cold and over 35 at idle at operating temperature, the problem pop out when engine turns close to 5000 rpm, the gauge pointer has a superfast vibration from around 5 to 35 PSI.
Cavitation?
Looking for the cause on the web i've seen that some oil pump has problem over 5000rpm or so, any experience with them?

i'll tear down oil pan to check pick up height first (honestly i want to see bearings too) then braze the pick up or make a bracket for it.

This is a mechanical gauge? Because if it's electrical, look for a bad connection.

The first thing I always look on ANY gauge when I get an abnormal, 'screwy' reading is the sender and the gauge. Check the pressure using another gauge, and check the connections, especially if you're using plastic tubing.

Cavitation IS what comes to mind, though. This is most often caused by the pickup being too close to the bottom of the pan rather than the PU being too high. And as you've suspected, the pump can pull air past a pressed on tube, although this isn't common especially if a new PU was pressed on correctly. But if the old PU was reused, or the job wasn't done just so, you can still pull air.

Use a good oil filter, too. The Fram filters have been reported to have problems associated w/pressure loss.

Not at all likely to be the problem, but still worth mentioning is the filter mount bypass. I like to block it off so the filter receives all the oil, but caution must be used when the oil is cold, and to keep an eye on the pressure- it will continue to drop as the filter becomes more and more restricted.

I've read lot of things on the forum about the causes of oil pressure drop, oil level, windage tray, oil pick up height and its related brazing to the pumo body can afflict pressure.
Mine is very good, about 70 when cold and over 35 at idle at operating temperature, the problem pop out when engine turns close to 5000 rpm, the gauge pointer has a superfast vibration from around 5 to 35 PSI.
Cavitation?
Looking for the cause on the web i've seen that some oil pump has problem over 5000rpm or so, any experience with them?

i'll tear down oil pan to check pick up height first (honestly i want to see bearings too) then braze the pick up or make a bracket for it.

It's not a for sure thing to say when the engine is running with no load on it. Engines make some pretty strange vibrations on the crank and when these are not damped by a damper on the front of the crank and either a flywheel/clutch assembly or torque converter on the other, these shakes can be transmitted into the cam via the timing set. These could excite the distributor gear to shake about in its clearance which would transfer the shake to the oil pump. But frankly I'd be surprised that the average oil pressure gauge would have time to respond.

I'd expect that this is either the bypass valve chattering or the pump gears doing the same, or the inlet pipe is shaking and drawing air on and off. This also could be too much or too little clearance of the pick-up to the bottom of the pan.

Chevy pump gear chatter is a common problem often fixed by milling a groove in the cover plate from the discharge side to the opposite side of the gear. The cause of this is the 7 tooth gear of the pump is just too close to a harmonic of the engine's firing order; plus the bypass returns to the inlet side of the pump so the pumps operating frequency which is imprinted on the oil outflow is fed back in to the inlet when the pressure bypass is operating. This can really shake the daylights out of the gears.

The Chevy inlet being pressed into the pump cover leaves a lot to be desired, I don't like friction fits, I've never seen them last. If this is leaking air the pump input will become unstable a condition that will worsen with RPM. The usual solutions are to braze the inlet to the cover, another thing I love is getting cast iron that hot, and using a brace to carry the structural loads of the pick up off the connection point.

Other things about the pickup is that it needs to have the anti-vortex cover with screen at the intake side. The needs to be from 3/16ths to 3/8ths inch off the bottom of the pan or 4.8 to 9.5 mm.

great responses guys, they're so much apprecciated.
i'd love to do the grove on the pump cover and try to avoid cavitation, i have to braze the pick up wich was new but i want to make sure no air will pass through the pipe.

This link shows the Pump Mods>> http://www.chevytech.info/2c63.html
Many Builders recommend just changing the oil Filter after Cam breakin to retain the ZDDP additives in the oil for a longer period.

great link, thank you, pump is down ready for the mods, problem is to make to vertical groove on the gear bore, i haven't the right tool for that, but grooves on the bottom are easier to do, do you think i can make just them? any con?
thank you.

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